Gas and liquid control systems are used in the semiconductor industry to supply process gases and liquids to semiconductor processing equipment. These systems typically comprise highly finished tubing extending between a supply of the process liquid or gas and the semiconductor processing equipment. The process liquids and gases are forced under pressure through the tubing, which necessarily exhibits a certain resistance to the flow therethrough, which resistance is a function of the cross-sectional area and length of the flow passage through the tubing, the internal finish thereof, etc. Valves are provided in these control systems for opening and closing the fluid passages therethrough and thereby controlling the flow of fluid from the supply to the semiconductor processing equipment.
A drawback or limitation of conventional valves used in these control systems is that, even in the open position of the valves, they provide an increased resistance to flow as compared with a piece of straight tubing or pipe of the same inner diameter as the inlet and outlet to the valve and the same length as the fluid passage through the valve. Cv is defined in the ANSI/ISA Control Valve Capacity Test Procedure as a measured number that is inversely proportional to the square root of the resistance to a given flow through a valve, regulator, tubing or similar device. For example, a ten inch long, 316L stainless steel or Hastelloy.RTM. C22.TM. tubing, having a one inch diameter, O.D., and an internal diameter, I.D., of 0.875 inch, whose internal surface is finely finished, .ltoreq.10 Ra micro inch, has a Cv of about 42. In contrast, with conventional bulk process valves of the same length, for example, for use with such tubing, the valves having this same internal diameter at their inlet and outlet as the tubing, the valves exhibit lower Cv's, 28-38 that is the Cv's of conventional bulk process valves are substantially lower, e.g., from about 10 to 33% lower than the Cv's of such tubing. Thus, the addition or substraction of a conventional valve to the tubing of a gas or liquid control system causes a change in pressure drop or flow restriction thereof. In the case of addition of a conventional valve, the pressures required to force the process gas or liquid through the control system, even with the valve open, is increased. There is a need for an improved, high Cv bulk process valve, control system and method which overcome this drawback or limitation of the conventional bulk process valves, control systems and methods such that the Cv of the bulk process valve is not substantially lower than the Cv of the tubing.